1. Field of the Invention
This invention relates, in general, to electrical apparatus and, more specifically, to fluid-filled tank structures for electrical apparatus.
2. Description of the Prior Art
Corrosion problems associated with the tanks of electrical apparatus seriously limit the useful life of such apparatus. In certain electrical apparatus, such as distribution transformers, this problem is aggravated due to the thinner materials of which the distribution transformer tanks are formed and, also, due to the highly corrosive environment such apparatus are placed in, such as those disposed in underground vaults or buried directly in the earth. The tanks of such apparatus must not only seal tightly to prevent leakage of the cooling medium and to keep water and other foreign materials out of the tank; but also must support the weight of the core and coil assembly and the cooling medium during shipping, handling and installation and withstand the dynamic forces exerted by the components of the transformer itself during its operation.
The conventional approach to corrosion prevention consists of coating the exterior tank surfaces with specially formulated coating materials. Protective coatings, however, are only as good as the uniformity of the coating with any pinholes or scratches in the coating, such as those due to shipping, handling and installation, causing rapid corrosion at these areas. Once the coating is damaged, corrosion is further promoted in certain areas, such as at the rim, by water dripping from the lowest extremity thereof.
The configuration of the joint or connection between the cylindrical side wall and the flat bottom members of the tank may also promote or be susceptible to corrosion. Certain prior art configurations, such as those having the joint located at the lowest extremity of the tank or those having the edge of the bottom member bent around the outer surface of the side wall and joined thereto, as shown in U.S. Pat. Nos. 1,699,434 and 3,907,152, are especially susceptible to early corrosion failure since the joint is located at the lowest extremity of the tank rim and thereby subject to the full force of the corrosive effects described above.
Thus, it would be desirable to provide a tank for a fluid-filled electrical apparatus that provides improved corrosion protection therefor. It would also be desirable to provide a substantially leakproof joint construction between the side and bottom members of a tank that easily accommodates the necessary welding or other joining technique to complete the joint and at the same time simplifies the necessary cleaning and finishing of the joint area. Finally, it would be desirable to provide a joint construction that provides easy assembly of the tank by tending to center the bottom member within the side wall member and, also, to constrain the side wall member in a cylindrical configuration.